With the development of information and communication technology, various wireless communication technologies are under development. Among these wireless communication technologies, a wireless local area network (WLAN) enables wireless connection to the Internet at homes or companies or in specific service provision areas using a portable terminal, such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP), based on radio frequency (RF) technology.
As standards for WLAN technology, the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards are under development. IEEE 802.11a provides a transmission speed of 54 Mbps using an unlicensed band at 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps using direct sequence spread spectrum (DSSS) at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps using orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps for four spatial streams using multiple-input multiple-output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidth up to 40 MHz and in this case, provides a transmission speed of 600 Mbps.
With the proliferation of such WLANs and the diversification of applications using WLANs, there is an increasing necessity for new WLAN technology for supporting a higher throughput than a data processing speed of IEEE 802.11n. Very high throughput (VHT) WLAN technology is one of the IEEE 802.11 WLAN technologies proposed to support a data processing speed of 1 Gbps or higher. Among these WLAN technologies, IEEE 802.11ac is being developed as a standard for providing VHT in a band of 6 GHz or lower, and IEEE 802.11ad is being developed as a standard for providing VHT in a 60-GHz band.
In a system based on such a WLAN technology, a terminal transmits a plurality of probe request frames to search for a plurality of APs. Therefore, power consumption increases, and it takes a long time to search for the APs.